1. Field of the Invention
The present invention relates to a mechanism for tilting and trimming an outboard engine mounted on a boat.
2. Description of the Prior Art
Small-size shims such as motorboats with outboard engines have a tilting and trimming device including a tilt cylinder for tilting the outboard engine upwardly out of and downwardly into the water, and trim cylinders for changing the angle of the outboard engine underwater. The tilt and trim cylinders are hydraulically operated under the pressure of working oil supplied from a pump.
The tilting and trimming device is capable of tilting down the outboard engine from a tilted-up position upwardly of the water. When the outboard engine is to be tilted down, if the trim cylinders were brought down prior to the tilt cylinder, the outboard engine would not contact the trim cylinders in a position where it should, and could not be adjusted in angle underwater. To avoid such a drawback, there has been proposed a tilting and trimming mechanism for preventing trim cylinders from moving downwardly prior to a tilt cylinder, as shown in FIGS. 7 and 8 of the accompanying drawings.
The proposed tilting and trimming mechanism operates to move the outboard engine upwardly as follows: As shown in FIG. 7, a pump 100 is rotated in one direction by a motor to discharge working oil from a port 100a to a lefthand pressure chamber 101a of a main valve 101. The oil pressure applied to the lefthand pressure chamber 101a opens a check valve 102, and also moves a spool 103 in the main valve 101 to the right, opening a check valve 104. The working oil supplied to the lefthand pressure chamber 101a is delivered through the check valve 102 and an oil passage 105 to a lower chamber 106a of a tilt cylinder 106 and also to lower chambers 107a of respective trim cylinders 107. Piston rods 106c, 107c of the tilt and trim cylinders 106, 107 are therefore pushed upwardly. Working oil in an upper chamber 106b of the tilt cylinder 106 is delivered through an oil passage 108, the check valve 104, and a righthand pressure chamber 101b of the main valve 101 into a port 100b of the pump 100. Working oil in upper chambers 107b of the respective trim cylinders 107 are drained into an oil tank 110 through an oil passage 109. At the same time, working oil is drawn from a tank 110 through an oil passage 111 into the pump 100 to make up for an oil shortage that is caused by the portions of the piston rods 106c, 107c which are displaced out of the tilt and trim cylinders 106, 107.
The tilting and trimming mechanism operates to move the outboard engine downwardly as follows: As shown in FIG. 8, the pump 100 is reversed, i.e., rotated in the opposite direction, to supply working oil from the tank 110 through an oil passage 112 to the righthand pressure chamber 101b of the main valve 101. The oil pressure applied to the righthand pressure chamber 101b opens the check valve 104, and also moves the spool 103 in the main valve 101 to the left, opening the check valve 102. When the pump 100 is continuously reversed, the working oil is delivered through the check valve 104 and the oil passage 108 to the upper chamber 106b of the tilt cylinder 106, whereupon the piston rod 106c is lowered.
At this time, the upper chambers 107b of the trim cylinders 107 are not supplied with working oil, and the working oil is not drawn out of the lower chambers 107a of the trim cylinders 107 as the pressure in the oil passage 105 produced with the working oil drawn out of the lower chamber 106a of the tile cylinder 106 exceedingly acts in the lower chambers 107a. Accordingly, only the working oil from the lower chamber 106a of the tilt cylinder 106 is supplied through the main valve 101 and the pump 100 to the upper chamber 106b, lowering the piston rod 106c.
As a result, the trim cylinders 107 are prevented from moving downwardly prior to the tilt cylinder 106. When the tilt cylinder 106 is contracted to a predetermined position, the piston rods 107c of the trim cylinders 107 come into engagement with portions 113 of the outboard engine. Subsequently, the piston rods 107c are lowered by the portions 103 of the outboard engine, forcing the working oil to flow from the lower chambers 107a through the oil passage 105 and the check valve 102 to the pump 100. The upper chambers 107b draw working oil from the tank 110 through the oil passage 109. Any excess working oil flowing from the tilt and trim cylinders 106, 107 returns to the tank 110 through a down-blow valve 116.
While the outboard engine is being kept in the tilted-up position for a long period of time as when the motorboat is moored, if the piston rods 107c remained projected out, shellfishes would tend to attach to and rust would tend to develop on the piston rods 107c. According to the customary practice, when the outboard engine is to be kept in the tilted-up position, the outboard engine is locked against downward movement by a suitable lock, and a manual valve 114 is opened and the piston rods 107c are manually pushed into the trim cylinder 107.
As described above, the conventional tilting and trimming mechanism is effective to prevent the trim cylinders 107 from moving downwardly prior to the tilt cylinder 106. However, it is tedious and time-consuming to manually lower the piston rods 107c as when the motorboat is moored.